1. Field of the Invention
The present invention relates to a semiconductor laser driving apparatus, which drives a semiconductor laser (laser diode), and a laser scanner including the semiconductor laser driving apparatus. Especially, the present invention relates to a driving control of the semiconductor laser for the scanning.
2. Description of the Related Art
A laser scanner including a semiconductor laser, which is incorporated in a laser printer, an electronic photograph system and so on, performs scanning by controlling the emission of laser beams, whereby a printing or copying is performed. When a pulsed driving current is fed to the laser diode in accordance with pattern-forming data, the laser beam is emitted from the laser diode at a given timing. The laser beam is deflected by an optical system for scanning, so that a photosensitive body, such as a photosensitive drum, is scanned and a design pattern is formed on the photosensitive body. In recent years, various laser diodes, having different wavelength, have been developed, and a laser diode with suitable characteristics for the photosensitive body is selected and used.
The response characteristics of the laser diode to the pulsed driving current, namely, the characteristics of the output pulse of the laser beam, are different for each laser diode. Especially, in the case of a laser diode with a wavelength in the vicinity of ultraviolet rays, a phenomena where there is a rise in light-emission delay time, occurs when the driving current is supplied. This phenomenon causes a lack of exposure of one-dot on the photosensitive body.
In recent years, scanning at higher speeds has been required, and the exposure time for one-dot has become even shorter. Especially, when performing a half-gray printing at high speed, a minute adjustment of the exposure is required. In the case of printing at high speed, the rate at which the driving current is switched ON and OFF has become much higher, and disturbance of the driving current occurs in the transient state. A remarkable decrease in density occurs because of the delay in the light-emission, so that the quality of the image output from the electronic photograph system or the quality of the printed image degrades.
Therefore, an object of the present invention is to provide a semiconductor laser driving apparatus and a laser scanner that are capable of properly controlling the emission of the laser beam in a scanning operation.
A semiconductor laser driving apparatus of the present invention is incorporated in a laser printer, an electronic photograph system such as a digital copy machine, and so on. The semiconductor laser driving apparatus has a laser diode, a laser driving circuit, a conductor, and an inductance adjuster. The laser diode, namely, the semiconductor diode, emits a laser beam. The laser driving circuit drives the laser diode by feeding a driving current in pulses to the laser diode. Thus, the laser diode emits the laser beam in pulses. The conductor conducts the driving current from the laser driving circuit to the laser diode. The inductance adjuster has a conductor-pattern for conducting the driving current and adjusting the magnitude of inductance in the conductor.
According to the present invention, a part of the conductor-pattern is selectively defined from the total of the conductor-pattern in accordance with the utilized laser diode. The defined part of the conductor-pattern conducts the driving current as a part of the conductor. The defined part of the conductor-pattern makes the magnitude of inductance a proper magnitude, which enables the laser beam to be emitted in generally rectangular pulses. Especially, the part of the conductor-pattern is selectively defined such that an output pulse of the laser beam takes on a generally rectangular form at a rising time.
When increasing the magnitude of inductance, a remarkable amount of so called xe2x80x9cover shootxe2x80x9d occurs in the driving current due to the high frequency of the driving current pulses. In the present invention, a waveform of the output pulse of the laser beam is adjusted by utilizing the xe2x80x9covershootxe2x80x9d, namely, the increase of the magnitude of inductance.
Since the magnitude of inductance can be adjusted to a magnitude suitable for the response characteristics of the incorporated laser diode (in other words, the output pulse characteristics of the laser beam), a lack of exposure does not occur even when printing and copying at high speed, so that high-quality images are obtained for every laser diode.
For example, when the laser diode and the laser driving circuit are provided on a printed circuit board, then the conductor is a wire that is formed on the printed circuit board, and the conductor-pattern is a wire-pattern that is formed on the printed circuit board. In this case, the inductance adjuster is formed on the printed circuit board during the manufacturing process. When the laser diode is exchanged, the magnitude of inductance is adjusted in accordance with the response characteristics of the newly incorporated laser diode. Then, a part of the wire-pattern, which is selected from the total of the wire-pattern, conducts the driving current as a part of the wire.
Preferably, the wire-pattern is formed in such a manner that the total-length of the wire varies in accordance with the selection of the part of the wire-pattern. Further, the wire-pattern is formed in such a manner that the width of the wire varies in accordance with the selection of the part of the wire-pattern.
A laser scanner of the present invention has a laser diode that emits a laser beam, a laser driving circuit that drives the laser diode by feeding a driving current in pulses to the laser diode, the laser diode emitting the laser beam in pulses, a conductor that conducts the driving current from the laser driving circuit to the laser diode, an inductance adjuster that has a conductor-pattern for conducting the driving current and adjusting the magnitude of inductance in the conductor, and a scanning optical system that deflects the laser beam and directs the laser beam to a photosensitive body for scanning. Then, a part of the conductor-pattern that makes the magnitude of inductance a proper magnitude for emitting the laser beam in generally rectangular pulses, is selectively defined and conducts the driving current as a part of the conductor.
A semiconductor laser driving apparatus according to another aspect of the present invention has a laser diode that emits a laser beam, a laser driving circuit that drives the laser diode by feeding a driving current in pulses to the laser diode so that the laser diode emits the laser beam in pulses, a conductor that conducts the driving current from the laser driving circuit to the laser diode, and an impedance adjuster that has a conductor-pattern for conducting the driving current and adjusting the magnitude of impedance in the conductor. Then, part of the conductor-pattern that makes the magnitude of impedance a proper magnitude for emitting the laser beam in generally rectangular pulses, is selectively defined and conducts the driving current as a part of the conductor.
The impedance is adjusted by changing the total-length of the wire, namely, by changing the magnitude of inductance, or, the impedance is adjusted by changing the width of the wire, namely, by changing the magnitude of resistance.
The xe2x80x9cimpedancexe2x80x9d and xe2x80x9cinductancexe2x80x9d, described above, indicate impedance and inductance during the transient state that occurs in the circuit because of the driving current. Note that, the transient state occurs when the driving current for the laser diode is switched ON and OFF at high speed.